1. The Field of the Invention
The invention generally relates to the field of communication along a fiber-optic channel. More specifically, the invention relates to a device for transmitting data bi-directionally in a single fiber-optic cable.
2. The Relevant Technology
Digital data can be efficiently propagated through a fiber-optic cable using light signals from light emitting diodes or lasers. To send data on a fiber-optic cable, the data is typically converted from electronic data generated by computers to optical data that can be propagated onto the fiber-optic cable. When data is received from a fiber-optic cable, the data must be converted from optical data to electronic data so that it can received by a computer.
To convert electronic data to optical data for transmission on a fiber-optic cable, a transmitting optical subassembly (TOSA) is often used. A TOSA uses the electronic data to drive a laser diode or light emitting diode to generate the optical data. When optical data is converted to electronic data, a receiving optical subassembly (ROSA) is used. The ROSA has a photo diode that, in conjunction with other circuitry, converts the optical data to electronic data. Because most computers both transmit and receive data, most computers need both a TOSA and a ROSA to communicate through fiber-optic cables. A TOSA and ROSA can be combined into an assembly generally referred to as a transceiver. Current transceiver designs are accomplished by integrating a discrete TOSA with a discrete ROSA. Transceiver designs using discrete components suffer from drawbacks such as increased overall packaging, increased size, increased cost, decreased yield, and the like.
The transceiver typically accomplishes bi-directional communication through the use of two fiber-optic cables. A first cable is used to transmit data and a second cable is used to receive data. It is often desirable to limit the number of fiber-optic cables between two communication points to save on material costs and installation. One method of limiting the number of cables is by both sending and receiving data on the same fiber-optic cable, which is possible because of the directional nature of an optical signal that is propagated along a fiber-optic cable. Generally, achieving bi-directional communication on a single fiber-optic cable is done through the use of splitters or circulators.
A common splitter design is shown in FIG. 1. Splitter 100 includes input ports and output ports. As shown in FIG. 1, these ports are represented by pigtail leads. Pigtail 102 represents the transmission line of a communications transceiver. Pigtail 104 represents the receive line of the communications transceiver. Pigtail 106 is a fiber-optic cable to the communications network. Commonly, a transceiver sends optical signals through the transmission pigtail 102. The optical signal travels to a splitter plate 108, which splits the optical signal in two directions. In one example, approximately half of the optical signal is sent towards the decimation path 112. The remaining portion of the optical signal is propagated into the pigtail 106. Data being received by the splitter 100 travels through the pigtail 106 into the splitter 100. The splitter plate 108 reflects half of the light to the decimation path 112 and half of the light to the reflector 110. The reflector 110 reflects all of the light towards the reception pigtail 104. Any light reflected to the decimation path 112 is usually lost.
A 3 dB decimation represents approximately a half power drop at the splitter plate 108. Using a splitter to achieve bi-directional communication often results in reduced optical power. Some splitters, for example, experience around a 3 dB drop in power. For a transceiver pair (i.e. a transceiver at a first computer and a transceiver at a second computer that communicates with the first computer), the use of splitters may result in a loss of approximately 6 dB.
Another method of bi-directional communication along a single fiber-optic cable involves the use of optical circulators. An optical circulator is generally a device having three or more ports, by which optical data input into one port is output at the next port. When light is transmitted bi-directionally, a transceiver TOSA portion transmits optical data to port 1 where it is propagated onto the fiber-optic network at port 2. Optical data from the fiber-optic network comes through port 2 and is output to port 3 where the ROSA portion of the transceiver receives the optical data.
One drawback of using a conventional circulator for this type of communication is that such circulators are relatively expensive. Optical circulators are generally constructed using discrete components and each of these components typically has its own individual packaging and interfaces that need to be dealt with when they are combined together to form a circulator. Moreover, to enable such conventional circulators to be used in this way, there is a need to avoid significant near end back-reflection. In particular, the connectors need to be well connected and the back-reflection needs to be less than −35 dB in one example.
Although conceptually bi-directional communication can be accomplished using discrete transceivers and circulators or splitters, there are no such designs that package the circulator or splitter into a compact module as part of a transceiver. Thus, discrete components must be used. As such, it is not possible to reduce the overall packaging, decrease the overall footprint of the transceiver and circulator combination, reduce component count, increase yield, etc. An integrated transceiver design that allowed for bi-directional communication along a single fiber-optic cable would be beneficial.